This invention relates generally to magnetic encoders and, more particularly, to magnetic encoders for producing an index pulse in addition to a high resolution signal.
Normally in a rotary incremental encoder, when an index pulse is required, the encoder has a unique track for the index pulse function that is separate from the high resolution track. A separate sensor is used to sense the index pulse track. Such encoders may have an optical disk target for use with an optical sensor or a gear tooth wheel or magnet target for use with a magnetic sensor.
For magnetic encoders, the high resolution track and the index pulse track cannot be placed very close to each other because the magnetic field from the index pole would then interfere with the high resolution track. Specifically, the high resolution track on the encoder must be very precise. If a disturbing field (such as from an index pole) is placed near it, the precision will deteriorate in the vicinity of that disturbing field.
Thus, sensors used with magnetic encoders will produce a signal with only poor accuracy if the index track is placed near the high resolution track. As a result, magnetic encoders that have an index pulse must be relatively large to provide the distance needed between the two tracks. Additionally, there are many manufacturing problems with magnetizing an index pulse very near a magnetic high resolution track.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.